Random-anisotropy driven giant magnetic entropy change in first-order magnetic transition under external fields

Abstract

First-order magnetic transition (FOMT) and isothermal first-order magnetization process (FOMP) were investigated for a two-dimensional (2D) spin system using the Monte Carlo simulation for the spin S = 1 Blume-Capel model with random anisotropy in an external magnetic field. Within this framework, giant changes in isothermal magnetic entropy occur near the FOMT critical temperature $T_C^{\left(1\right)}$ when the magnitude of the random anisotropy D and its probability p is sufficiently large. The behavior of the FOMT is observed not only by a sudden drop of magnetic moment at a critical temperature $T_C^{\left(1\right)}$ but also by redistributing energy and magnetic moment histograms. From that, we successfully produce a phase diagram illustrating a random-anisotropy-driven second-order magnetic transition (SOMT) to FOMT in comparison with Ref. [1]. Magnetic entropy change (∣ΔS_M∣) calculations indicate that a giant magnetocaloric effect at a low magnetic field occurs very close to $T_C^{\left(1\right)}$ when its strength approaches the critical field h_cr of the FOMP. Besides, the ∣ΔS_M∣ in the FOMT is much larger than in the second-order magnetic transition at the same low field. We also conduct calculation comparisons about the temperature dependence of magnetic behavior near the FOMT with experimental observations for Cr₁₁Ge₁₉ samples.